1. Field of the Invention
The subject invention relates to a plate valve for use with reciprocating compressors, and more particularly to, a valve having a sealing plate with contoured sealing surfaces.
2. Background of the Related Art
Reciprocating compressors are positive-displacement machines which generally include a piston, a piston rod, a cylinder, at least one suction valve and at least one discharge valve. In reciprocating compression, a medium, usually gas or air, is compressed by trapping the medium in an enclosed cylinder and then decreasing its volume by the action of a piston moving inside the cylinder. The medium is compressed to a pressure sufficient to overcome the spring tension holding a discharge valve closed, at which time the discharge valve opens and allows the compressed medium to leave the cylinder.
Because of the nature of the reciprocating piston, compression ceases at the limits of its stroke, the discharge valve again closes due to the action of the springs on the valve, the piston reverses direction, and a small amount of medium remaining in the cylinder expands, increasing in volume and decreasing in pressure. When the inlet pressure is higher than the pressure inside the cylinder and the spring tension holding the suction valve closed, the suction valve then opens, allowing the medium to flow into the cylinder. At the opposite limit of the piston stroke, the suction valve closes due to the springs acting on the valve, the piston again reverses direction, and the compression cycle begins anew.
Of the many components in a reciprocating compressor, none work harder nor serve a more important function than the suction and discharge valves. In fact, compressor efficiency is determined by the performance of the valves more than any other component. For optimum compressing efficiency to be achieved, these valves must be configured to provide a maximum flow area while at the same time, the medium flow through the valve must meet with a minimum resistance. In addition, it is critical that valve closure prevent leakage of gas or air in either direction.
Many compressors are run at peak loads for weeks or months at a time with no relief. In a typical 1000 rpm compressor, the valves which operate automatically with every stroke of the piston, open and close almost three million times a day. Therefore, in order to achieve optimum compressor efficiency, valve design must meet the above-mentioned objectives of efficient medium flow and control.
Generally, a compressor valve (discharge or suction) is composed exteriorly by two components, namely a valve seat and a valve guard. The valve seat provides inlet flow ports for the medium. The interior surface of the valve seat defines what is traditionally termed the seating surfaces. The valve guard defines outlet flow ports and is typically secured to the valve seat by bolts or a central stud and is spaced therefrom. Internally, the compressor valve is composed of a sealing plate or a series of rings and biasing elements such as helical springs. The sealing plate is disposed in the space between the valve seat and valve guard and is axially movable therein. The surfaces of the plate or rings which are located adjacent to the valve seat are termed sealing surfaces. These surfaces are designed to be engaged with corresponding seating surfaces of the valve seat. A biasing element is disposed between the valve guard and the sealing plate, urging the sealing plate sealing surfaces into a sealing engagement with the seating surface of the valve seat. In this biased position, the medium is prevented from flowing through the valve. As mentioned previously, when the operation of the compressor is such that sufficient pressure exists to overcome the force applied to the sealing plate by the biasing element, the valve will open allowing medium to flow into or out of the compressor cylinder.
The configuration of the sealing plate sealing surfaces and their engagement with the valve seat can have a dramatic impact on the flow of medium through the valve. In the compressor valves commonly in use today, there is an appreciable velocity head loss occasioned by problems in moving the fluid through the valve at high velocity. The problems are largely caused by energy losses resulting from extreme changes in flow direction, frictional interference and turbulence by the fluid as it passes through the compressor valve, around the sealing surfaces. These problems are especially critical in attempting to obtain optimum efficiency and capacity in high speed compressors undergoing 800 to 4000 strokes of the piston per minute.
In addition, configuration of the sealing plate sealing surfaces and their engagement with the valve seat can significantly impact the ability to prevent leakage of medium in either direction when the valve is in the closed position. Performance of the compressors, which by their nature have a very short stroke, requires valves which not only permit flow of the fluid or gases to and from the cylinder with a minimum of pressure loss and at a high velocity, but which will also seat rapidly and positively during the critical pressure reversals which take place at the beginning and end of the intake and discharge strokes.
Traditionally, a sealing plate for a compressor valve consisted of a circular plate that had opposed planar surfaces with flow ports extending between the opposed surfaces. For these valves the seating surfaces were planar and did not protrude into the flow ports of the valve seat, but merely covered the ports. U.S. Pat. No. 3,123,095 to Kohler discloses a plate valve with a sealing plate having planar seating surfaces. A disadvantage to this configuration, as well as others having planar sealing surfaces, is that flow through the valve tends to be turbulent resulting in increased pressure loss across the valve. The turbulence is caused by the rapid change in the direction of flow through the valve. In compressor valves, the flow ports of the sealing plate and the valve guard are aligned, but for obvious reasons these ports are offset from the inlet ports of the valve seat. As a result, the flow proceeds into the valve through the valve seat and must rapidly change direction in order to traverse to the ports in the sealing plate. This rapid change in direction results in the turbulent flow.
In an effort to improve the flow through the valve, sealing plates were furnished with profiled sealing surfaces which facilitate the flow through the valve by providing a smoother transition from the inlet flow ports of the valve seat to the flow ports of the sealing plate and valve guard. U.S. Pat. Nos. 3,536,094 to Manley discloses a prior art compressor valve having a sealing plate or rings with profiled sealing surfaces. The sealing surfaces in the Manley patent have a convex spherical cross-section which engages in concave spherical seating surfaces in order to interrupt the flow through the valve.
U.S. Pat. Nos. 4,924,906 and 5,052,434 to Harbal and Bauer receptively, also disclose valves with profiled sealing surfaces. Both of these patents disclose sealing surfaces that can be provided in a variety of cross-sections and engage in corresponding recesses in the valve seat. The Hrabal patent uses sealing rings which have a profiled cross-section and a support plate as the means for restricting and directing flow through the valve. The Bauer patent uses two piece rings of various cross-section to facilitate valve flow and closure.
The disclosures in the Manley, Harbal and Bauer patents attempt to provide a compressor valve that minimizes the velocity and pressure loss through the valve and increase the compressor efficiency by profiling the sealing surfaces. A disadvantage to these configurations is that the improvement in flow through the valve is achieved at the expense of valve seating performance. As noted, the optimum performance of the compressor requires valves which not only permit flow of the fluid or gases to and from the cylinder at a high velocity with a minimum amount of pressure loss, but which will also seat rapidly and reliably. The use of profiled sealing surfaces which are designed to mate with a corresponding profiled seating surface results in surface to surface contact (a surface contact condition). Having surfaces that mate reduces the contact pressure associated with the engagement of these surfaces and in turn reduces the reliability of the seal.
More specifically, contact pressure is a function of the contact force applied divided by the area of contact. The higher the contact pressure, the more reliable the seal. In compressor valves, the contact force is a result of the differential pressure across the valve and is primarily equal to the force exerted by the biasing element and has a constant magnitude. As a result, the only way to increase the contact pressure is to reduce the area of contact. It has been shown that a more reliable and rapid valve closure is achieved when the surfaces do not mate and the engagement between the sealing and seating surfaces occurs along a continuous line of contact.
There is a need, therefore, for a new valve which improves the flow of medium through the valve by providing a smoother transition from the inlet flow ports of the valve seat to the flow ports of the sealing plate and valve guard while at the same time improving the reliability of the seat engagement by increasing the engagement contact pressure.
The subject application is directed to a new and improved valve for use with reciprocating compressors, and more particularly to, a compressor valve having a sealing plate with contoured sealing surfaces, a valve seat, a valve guard and at least one biasing element for urging the sealing plate into engagement with the valve seat.
The valve seat has opposed upper and lower surfaces and defines inlet flow ports. The inlet flow ports extend between the upper and lower surfaces and provide a path for admitting a controlled medium into the valve. The lower surface of the valve seat includes at least one seating surface. The valve guard has a recessed area with opposed upper and lower surfaces and defines outlet flow ports. The outlet flow ports extend between the upper and lower surfaces of the valve guard and provide a path for discharging a controlled medium from the valve. The valve guard is secured to the valve seat and spaced therefrom to enclose the recessed area and define a cavity therebetween.
In accordance with the subject application, the sealing plate has opposed upper and lower surfaces and defines flow ports which extend between the upper and lower surfaces for facilitating flow of a controlled medium through the valve. The sealing plate is positioned within the cavity and moves relative to the lower surface of the valve seat between an open and closed position. In the open position the sealing plate is spaced from the lower surface of the valve seat so as to permit medium flow through the inlet flow ports of the valve seat and in the closed position the sealing plate is engaged with the valve seat so as to prevent medium flow through the valve. The upper surface of the sealing plate defines at least one contoured sealing surface for engaging the at least one contoured seating surface of the valve seat along a continuous line of contact when the valve is in the closed position.
Preferably, at least one biasing element is disposed between the valve guard and the sealing plate, for urging the sealing plate into the closed position. The biasing element is engaged within a corresponding recess in the valve guard. It is envisioned that at least one seating surface of the valve seat includes inclined surfaces oriented relative to the lower surface of the valve seat, wherein the angle of inclination of the inclined surfaces is about between 0 degrees and 90 degrees relative to the lower surface of the valve seat.
Preferably the contoured sealing surface of the sealing plate includes inclined surfaces oriented with respect to the upper surface of the sealing plate, wherein the angle of inclination of the inclined surfaces is about between 55 and about 20 degrees. It is also envisioned the angle of inclination of the inclined surfaces of the valve seat and the angle of inclination of the valve plate can differ from each other by about between 0 degrees and 10 degrees. Preferably, the angle of inclination of the inclined surfaces of the valve seat and the angle of inclination of the valve plate differ from each other by about 3 degrees. In a preferred embodiment of the subject application, the contoured sealing surface of the sealing plate includes curved surfaces for achieving line contact with a valve seat seating surface.
It is envisioned that the sealing plate of the subject invention is formed from a metallic material such as stainless steel, alloy steel, Inconel or titanium. Alternatively, the sealing plate may be formed from an non-metalic material (e.g., a thermoplastic, a thermoset, etc.) or a composite material (either reinforced or non-reinforced), or a material exhibiting substantially similar strength and flexural properties.
The subject invention is also directed to a compressor valve which includes a valve seat, valve guard, at least one biasing element and a sealing plate having first and second contoured sealing rings. The valve seat has opposed upper and lower surfaces and defines arcuate inlet flow ports for admitting a controlled medium. The inlet flow ports extend between the upper and lower surfaces, and the lower surface has first and second, seating surfaces. The valve further includes a valve guard which has a recessed area with opposed upper and lower surfaces. The arcuate outlet flow ports extend between the upper and lower surfaces and provide a path for discharging the medium from the valve. The valve guard is secured to the valve seat and spaced therefrom to enclose the recessed area and define a cavity therebetween.
The sealing plate has opposed upper and lower surfaces and defines arcuate flow ports. The arcuate flow ports extend between the upper and lower surfaces for facilitating flow of medium through the valve. The sealing plate is mounted for movement within the cavity and relative to the lower surface of the valve seat between an open position and closed position. As noted above, the upper surface of the sealing plate defines first and second contoured sealing rings for engaging the first and second seating surfaces of the valve seat along a continuous line of contact when the valve is in the closed position.
The subject invention is also directed to a sealing plate for a compressor valve which includes a valve seat defining inlet flow ports and a valve guard defining outlet flow ports. The sealing plate includes a body having opposed upper and lower surfaces and defines flow ports extending between the upper and lower surfaces for facilitating flow of a controlled medium through the valve. The upper surface of the sealing plate defines at least one contoured sealing surface which engages at least one seating surface of a valve seat when the valve is biased into a closed position thereby, preventing the flow of a controlled medium through the valve. The contoured sealing surfaces have a cross-sectional configuration that is adapted and configured to achieve continuous line contact with the valve seat seating surfaces when the valve is in the closed position.
Those skilled in the art will readily appreciate that the subject invention improves the flow of medium through the valve by providing a smoother transition from the inlet flow ports of the valve seat to the flow ports of the sealing plate and valve guard and improves the reliability of the seat engagement by increasing the engagement contact pressure.
These and other unique features of the valve disclosed herein will become more readily apparent from the following description, the accompanying drawings and the appended claims.